ch32.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

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		<TD ALIGN="LEFT">Menu </TD>

		<TD ALIGN="LEFT">Objects derived from <TT>OI_menu</TT> </TD>

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</CENTER>

<CENTER>

<H3><A NAME="Heading27<FONT COLOR="#000077">How to Create an Application</FONT></H3>

</CENTER>

<P>The first step to creating an application is to invoke ObjectBuilder in a new

or empty directory. Once the main window appears, move the window to a convenient

area of the screen.</P>

<P>Next, open the Palette menu and select a palette from the Palettes pull-right

menu shown in Figure 32.8. The palette window opens, displaying all possible objects

for that palette. For beginners, the Novice palette is the simplest to use. The Novice

palette window is shown in Figure 32.16. 



<P>

<a href="../art/32/32fig16.gif">Figure 32.16.</A> The Novice palette window.



<P>The application window is usually the top-level or root object of an application.

Select the application window object and drag it to an empty location on your screen.

This window can now be resized to what is appropriate for your application.</P>

<P>You can now select and drag each required object into the application window.

Once all the objects needed have been created you can close the Palette window by

selecting Close/Dismiss from the Palette window's File menu.

<CENTER>

<H4><A NAME="Heading28<FONT COLOR="#000077">The Attribute Editor</FONT></H4>

</CENTER>

<P>The Attribute Editor allows you to modify specific attributes or resources for

each object. To invoke the editor, move the pointer to an object you want to modify

and double-click the Select mouse button. An Attribute Editor similar to the one

shown in Figure 32.17 is displayed. 



<P>

<a href="../art/32/32fig17.gif">Figure 32.17.</a> The Attribute Editor.



<P>The Attribute Editor appears with the name of the object being modified in the

title bar. Depending on the object that is to be modified, the Attribute Editor displays

different resources.</P>

<P>ObjectBuilder assigns an internal name to all of your objects. If you modify the

Object Name resource (which is recommended because the names that ObjectBuilder assigns

are not very intuitive) ObjectBuilder still maintains its internal name for the object.

This name is displayed in the title bar of the Attribute Editor when you are editing

the object.



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<DL>

	<DD>

<HR>

<A NAME="Heading29<FONT COLOR="#000077"><B>NOTE:</B> </FONT>ObjectBuilder may

	not interact perfectly with the <TT>fvwm</TT> window manager that comes with Linux.

	Some of the windows do not appear with title bars. To see the information, such as

	the object name, that is being displayed in the title bar, switch to one of the other

	window managers.

<HR>



</DL>



<P>The attributes that are common to all objects are Category, Object Name, Apply

To, and Title. When the Editor appears, the Category is set to <TT>default</TT>.

If the Category is not <TT>default</TT>, or you want another category, press the

abbreviated menu button to display a list of categories from which to choose. The

category tells you what the attributes or resources are for. <TT>Default</TT> is

the object as viewed, and <TT>callback</TT> defines the action that occurs in response

to an event for that object.</P>



<P>The Apply To resource lets you choose whether the modifications apply only to

that object, to the object and its children, or siblings as well. There are numerous

combinations to choose from in this menu.</P>

<P>The Title resource is the title for the window. Modifying this changes what is

seen in the title bar of the window.</P>

<P>To ensure that the objects in an application window remain in the correct place

relative to their siblings, you must set a layout method for that object. Select

the Layout menu from the application window's Attribute Editor and view the layout

options, as shown in Figure 32.18. 



<P>

<a href="../art/32/32fig18.gif">Figure 32.18.</a> The Layout menu.



<P>Select an appropriate layout, and the objects in the application are moved. After

this the objects within the application window can still be moved but that movement

is restricted to within the boundaries of their parents.</P>

<P>When modifying resources for menu objects or menu cells, you need to specify whether

ObjectBuilder should perform the action on the menu or the menu cell by making a

selection in the Menu Focus option of the main window.</P>

<P>The Label Resource is the text that appears in a menu cell. The <TT>cbCellAction</TT>

resource assigns callback functions to the cell.</P>

<P>By selecting the Traverse pull-down menu from the menu bar at the top of the Attribute

Editor, you can shift the focus of the editor to a parent, child, or sibling of the

present object. This allows you to modify the resources of a child without affecting

the resources of the parent. The Traverse menu is shown in Figure 32.19.</P>

<P>If the Attribute Editor is open and you wish to modify the attributes of a different

object, place the pointer on the desired object and press the Select mouse button.

This causes the editor to display the resources for the selected object.</P>

<P>Because each object has a unique set of resources available to it that are too

numerous to mention here, they are explained in the Help function of ObjectBuilder.



<P>

<a href="../art/32/32fig19.gif">Figure 32.19.</a> The Traverse menu.



<P><CENTER>

<H4><A NAME="Heading30<FONT COLOR="#000077">Generating Application Files</FONT></H4>

</CENTER>

<CENTER>

<H4><FONT COLOR="#000077"><BR>

Generating Application Files</FONT></H4>

</CENTER>

<P>When you use ObjectBuilder to generate an application, it creates a number of

files for you. It is important to understand what each of these files is and what

they are used for. The files that are created and their purpose are listed here.

Configuration File (<TT>appname.cf</TT>)--This file contains the hierarchical description

of the graphical objects that make up the front end of the application. It also contains

the resource definitions and callback information for the objects.</P>

<P>Help File (<TT>appname.hp</TT>)--This file contains the application's context-sensitive

help.</P>

<P>Main Program (<TT>appname.C</TT>)--This file contains the code to handle the initialization,

user interaction startup, and OI cleanup. This file can be edited after it is generated

and ObjectBuilder will not overwrite any changes made to it.</P>

<P>Main Header File (<TT>appname.H</TT>)--This file is included in all ObjectBuilder-generated

C++ source code files. It can be edited after it is generated and ObjectBuilder will

not overwrite it.</P>

<P>External References Include File (<TT>appname_bd.H</TT>)--This file contains references

to all objects for which you requested user variables.</P>

<P>Binding File (<TT>appname_bd.C</TT>)--This file contains the object variables,

external declarations for all callback stubs, and a binding table that binds the

name of the object listed in the configuration file to the object itself.</P>

<P>Callback Stubs File (<TT>appname_cb.C</TT>)--This file contains fully documented

callback stubs generated by ObjectBuilder for all the callbacks according to the

specifications you entered in the Attribute Editor. The top portion of the file is

declarations and the bottom contains the callback stubs. There is a separator line

between the two sections that must not be removed. If you delete a callback, the

stub is deleted but you have to remove the declaration yourself. This file can be

edited, and ObjectBuilder will not overwrite any changes made.





<BLOCKQUOTE>

	<P>Makefile--This file provides instructions on how to build the application at runtime.

	It can be edited and ObjectBuilder will not overwrite the changes made.



</BLOCKQUOTE>



<P>Once the application is saved using the Save function from the File menu, the

above files are generated and placed in the same directory that ObjectBuilder was

originally started from. You can then use any text editor to edit those files that

require changes.

<CENTER>

<H4><A NAME="Heading31<FONT COLOR="#000077">Writing Callbacks</FONT></H4>

</CENTER>

<P>Applications created using ObjectBuilder are event driven. This means that code

is executed in response to an event. Here are examples of events:



<UL>

	<LI>Pressing a button

	<P>

	<LI>Selecting from a menu

	<P>

	<LI>Closing a window

	<P>

	<LI>Selecting an option

</UL>



<P>For your application to work you have to create the back end. The back end is

the code that tells your application what to do when an event, such as a selection

from a menu, occurs. ObjectBuilder refers to this code as a callback.</P>

<P>ObjectBuilder generates the callback stubs file according to the specifications

you give in the callback category of the Attribute Editor. Each callback has three

parameter entry fields. These fields specify the callback object, function, and argument,

going from left to right in the editor. Only the function is mandatory. The Attribute

Editor for the callback category of a menu cell is shown in Figure 32.20. 



<P>

<a href="../art/32/32fig20.gif">Figure

32.20.</A> The callback category. 





<P>The <TT>callback</TT> object is the object that is

used when calling a member function for a specific class. It is good practice to

allow runtime resolution of the object needed by a member function. The function

can be a member function or a stand-alone function. The arguments can be strings,

constants, or pointers to objects. Structures, floating point numbers, and pointers

to member functions cannot be passed as arguments. These are the rules for entering

arguments:



<UL>

	<LI>Strings are always quoted.

	<P>

	<LI>Constants are preceded by <TT>#</TT> and must be defined in the header file.

	<P>

	<LI>Pointers to objects are simply the object's name.

</UL>



<P>Each type of callback requires a different set of parameters. The parameters needed

for each callback are documented in the &quot;OI Programming Guide&quot; available

from ParcPlace Systems.</P>

<P>Once a callback function has been specified and the application is saved, ObjectBuilder

updates the binding table in the binding file. This table tells the application which

external functions to call when the button is pressed or menu item is selected at

runtime. ObjectBuilder generates a function declaration and a callback stub in the

callback<TT> </TT>stubs file. In the configuration file one statement is generated

that states the specific callbacks for an object and a second that provides directions

for satisfying those callbacks when the application runs.</P>

<P>You must add the C code for the functions to the callback stubs file (<TT>appname_cb.C</TT>)

using any text editor.

<CENTER>

<H4><A NAME="Heading32<FONT COLOR="#000077">Compiling and Testing the Application</FONT></H4>

</CENTER>

<P>Once the callback functions have been written you must compile and link the application

to the <TT>OI_Library</TT> files. First make sure that the makefile can find any

include files that are needed, as well as the <TT>OI_Library</TT> files, by editing

the following statements in the makefile. You need to do this only if the include

and OI files are not in the same directory as the application.<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">INC = $$OI_LIB/../../include

OILIB = -L$$OI_LIB/../-1OI

</FONT></PRE>

<P>The <TT>$$</TT> ensures that the environment variable <TT>OI_LIB</TT> is used

to find the libraries and the include files.</P>

<P>Compile and link the application by typing the following command in the directory

where the application was saved:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">make

</FONT></PRE>

<P>When this finishes, you can run the application by typing the application name

at the prompt.</P>

<P>If you want to make any changes, simply load the application into ObjectBuilder

using the following command:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">uib appname

</FONT></PRE>

<CENTER>

<H3><A NAME="Heading33<FONT COLOR="#000077">Summary</FONT></H3>

</CENTER>

<P>The visual aspect of ObjectBuilder enables you to drag and drop objects and their

resources into your application. ObjectBuilder does the rest of your user interface

development by generating C code to produce the behavior and appearance of the objects

that you put into your application. This saves you a great deal of time because a

significant amount of the entire development of an application is spent on the user

interface.</P>

<P>ObjectBuilder further helps you by defining the skeleton for the rest of the application.

Although you still have to write the core of your application, using ObjectBuilder

can save you vast amounts of time. Once you know the basic objects available in the

OI library and their hierarchy, creating a GUI or front end for an X Window application

using ObjectBuilder is simple.









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